Telegraphic repeater system



Sept 22, 1936- K. ETZRODT ET AL 2,055,343

TELEGRAPHIC REPEATER SYSTEM Filed May 21, 1952 Patented Sept. 22, 1936VPA'lENT OFFICE 7 REPEATER SYSTEM Karl Etzrodt,

Berlin- Siemensstadt,

Heinrich Flling, Berlin-Charlottenburg, and Walter Hhnle,Berlin-Siemensstadt,

Germany, as-

lsignersA to Siemens & Halske, Aktiengesell- V schaft, Siemensstadt nearBerlin, Germany, a

corporation of Germany Application May 21, 1932, serial No. 612,756 InGermany May 23, 1931 16 Claims.

Our invention'relates to a telegraphic repeaterl system, andmoreparticularly to a repeater system for wire telegraphy employingimpulses of different polarity and telephone repeaters having ampliercharacteristics. Y

VIn wire telegraphy employing impulses of different polarity effects ofdisturbing currents are more noticeable than in ordinary telegraphy.Special attention must, in particular, be paid to the high voltagesliable to injure attendants or operators. It would, in itself, bepossible to render the telegraph apparatus high-tensionproof, as hasbeen done in sectionalized telephony, for instance. -This is, however,unsuitable for telegraphy, as it would then be necessary to abandon thecustomary construction of the racks, in which the individual parts andrelays are so arranged as to be readily accessible. Grounding provisionsat the lines would indeed also be as 29, safeguard against dangerousvoltages, but these,

due to the necessary ground-symmetrical arrangement, again causediiculties in the phantom utilization of telephony. In telephoniccommunication it is known to subdivide the line into sections and toblock or protect the apparatus at theends of the line against inducedvoltages by repeaters. A

`Such an expedient 'can be utilized in impulse telegraphy by sendingdirectcurrent impulses when .closing the key in the telegraphtransmitter. f- By the protecting repeater vor more properly transformerat the sending side the direct current' impulses 'are converted intopure impulses and sent over the line; at the receiving side the impulsesmayfthrough the protecting transformer located here be passed to a relayadjusted for impulse reception.- Wire telegraphy of the polar-duplex orbriefly called impulse type has, however, a number of drawbacks, themost prominent of which is that a comparatively small energy is sentover the lines, which consequently aremore liable to `be adverselyaffected by the switching `operations in neighboring high tension powerlines. VThe impulse 'peaks of impulse telegraphy, furthermore, moreeasily cause utter phenomena-more particularly in loading coils and thelike, than the currents-of the direct current telegraphy operating withsmaller amphtudes;4 l A,

According to our invention these drawbacks are eliminated and yet aprotection ofthe telegraph apparatus against high tension influences isobtained bythe sending and/or receiving apparats of .the telegraphsystem being guarded by thertransformers against disturbing voltages onthe line, and by providing apparatus for sending the telegraph signalsover the line in the `form of direct current impulses. This may, forinstance, be effected by operating with directeurrent in front of theprotective transformer (that is, on the input side) and connectingbehind the transformer, which resolves each direct current impulse intoimpulses of opposite direction or polarity, a relay, for instance, .withaV holding curr-ent winding Vwhose local circuit sends direct currentimpulses over the line. Such a system has, however, still thedisadvantage that the relay and the feeding battery, which 'directlygenerate the line currents, are still located on the side of thetransformer affected by the disturbing voltage, and therefore, in orderto prevent accidents,` must notbe accessible under normal conditions.

According to a further feature of our invention, the telegraph currentsare keyed as alternating currents and sent over the protectivetransformer: Beyond the protective transformer the alternating currentimpulses are converted by rectifiersf into direct current impulses,which are then sent over the line. On the receiving side the directcurrent impulses reach the protective transformer on the input orreceiving side and are there resolved into impulses which operate thereceiving relay, if desired after amplification.

' In the drawing aixed hereto- Fig. 1 illustrates the principle of theinvention with reference to a telegraph apparatus operatingl on thepolar-duplex wire system and impulse reception; Fig. 2 is a partialdiagram of another embodiment, and Fig. 3 is a diagram of a thirdembodiment.

Referring to Fig. 1, alternating current is ac-i cording to theinvention sent, by closing thekey S, to the protecting transformer orstopper transformer U1 for which alternating current is Ysupplied to therectier system g'. The rectifier sys-- tem effects a completerectification. In this system direct current impulses are generatedwhich pass through the lter Fi to the line l. Hence they are passedthrough a filter F2 to the stopper transformer U2, which converts theminto impulses (two of opposite direction for one signal), which reachthe impulse relay R. At t We have indicated the telephone connections orcables. In the repeater system according to Fig. 1 each disturbingimpulse is, due to the construction of the transformer, resolved intotwo impulses ofl opposite direction which follow each other directly.

Contrary to Fig. 2 each disturbing impulse is,

` sufficiently accurate.

however,` dueV to the design of the transformer U2, resolved into twoimpulses of opposite direction, which follow each other directly, asdistinguished from the telegraph currents, whose impulses ofoppositedirection are separated by the duration of asignal. The effect ofdisturbing impulses may thus be reduced to the minimum length of thesignal by adjusting the time con-L stant of the relay R.

In the system illustrated in Fig. 1 an impulse amplifier may naturallybe connected up ahead of the receiving relay R. v

Such a wrong operation of the receiving relays may, however, to agreater extent be avoided by leading the direct current impulsesarriving from thel line to an apparatus which converts them intoalternating current impulses, which reach the receiving apparatusthrough the Vstopper transformer. Y

According to our invention this is preferably effected by leading thedirect current impulses into a magnetic amplifier consisting of a chokeor a rejector circuit, which is fed from a source of'alternating currentof higher frequency than the impulse frequency. Magnetic amplifiers.have: in comparison with valve amplifiers the great advantage that theyreproduce the low frequencies very well, and are thus particularlyuseful for the amplification of the impulsev telegraphy'signals. Theyare, furthermore, not so sensitive tov the replacement of circuitelements as valvefamplifiers; Valve amplifiers cannot be usedsimultaneously in both trafiic directions, as the: amplifiers of thetransmission direction block the amplifiers of the opposite direction.

According to our invention av magnetic amplifier is employed as atransmitting and asta receiving amplifier respectively' or as anintermediate amplifier, the windings of which are so designed and soconnected to the duplex line serving for the transmission of the signalsin the lines leading tothe transmitting and receiving apparatus, thattogether with a balancing network of the transmission line it functionsas a balancing repeater between the three lines. In thisway a two-wireor forked repeater for telegraphy may be built up which corresponds withthe.twowire intermediate repeaters and forked repeaters in telephonesystems. By the application of the iron repeaters. the above-mentioneddrawbacks of the valve amplifiers are eliminated.

,Thejrepeater or transformer according to the invention isY furthermoreat the same time available: for bothrdirections of traffic..vTransmitting and receiving circuits may be completely uncoupled providedthe artificial balancing line is The magnetic amplifiers consist intheir simplest designV of an iron-containing choke coil, which isconnected in an alternating current circuit whose frequency is higherthan the highest frequency to be amplified. TheY iron choke coil is soVmagnetically "loi biased by direct current, that it varies itsalternating current resistance when the low frequency volta-ges to be'amplified are applied with the frequency l of Ythese voltages. Thiscauses a modulation of the alternating current of the highervfrequencies. After the rectification of the modulated carrier ffrequencythe amplified low frequency is obtained.

By the introduction of the rectiflers, which arev necessary when Vmakinguse of magnetic amplifiers, anew phenomenon appears as compared with thenormal balancing connections,

T5 ,suchasLarerused in Y.telephone systems,for ini rectifier, i. e. withthe cadence of the outgoing current. This phenomenon causes the incomingcurrent to be modulated by the outgoing current.

According to. a further feature of our invention this modulation effectis reduced by the outgoing current notV being reduced to Zero andVpreferably being at al1 times maintained larger than '1% of its maximumvalue.

The modulation effect is not entirely prevented in this way, it is true,but confined within limits which according to; experience generally donot cause any disturbances of the telegraph service. The desiredcontrol' of the modulation effect may, for instance, be attained in thetransmitterby a bridging resistance for the transmitter key, and in the.

telephone repeater by the choice` of a correspond-v: If the modulationstillv continues to cause disturbances in spite of. theseing biasmagnetization.

expedients, an attenuation memben, preferably adjustablamay according,to a. further feature of' our invention be connected behind therectifier. the resistance of which,y is; so proportioned that thevariation of the impedance of the rectifier no longer plays an importantpart. The .attenua-- tion member mayA at the same timer be designed as acorrecting device for controlling the` frequencies of the vtelephonerepeater.

The incoming currenttaken up bythe rectifier represents an additionalload on the transmission line. If for any reason it is desirable toreduce this load, our invention provides for the cornpensation of thisdirect current by an additiona source of direct current.

As distinguished from the telephone repeaters the risk ofself-excitation in the telegraph yrepeater can be reduced bythe choiceof a repeater or transformer characteristic which is not linear in adefinite way. Such a non-linearity of the characteristic exists in anideal way in every contact relay. In this relay the amplification iszero up to reaching the limit of response and then rises to a very highvalue. at the moment. of reversal. In a repeater or transformer withsuch a non-linear characteristic a resonant rise-- of oscillations forself-excitation is impossible, be.- cause the current due to faultybalancing returned into the input circuit of the repeater is locatedbelow the threshold of response. In magnetic telephone repeaters asimilarV characteristic may be obtained by asuitable-,biasing of' therectifier with a direct current voltage,` fori instance, and thus thetendency to recoupling be reduced. This result may also be attained. byashunt consisting of a one-way ,rectifier 1ocated behind the rectifier,ther one-Way rectifier; being biased in such a way that it operates inthe: lower bend of its current. voltage-characteristic. A similar effectmay also be attained by choosing the magnetic conditions of thetelephone repeater in such a way that in case of low modulation theamplification is small, and large in arrangement according to ourinvention applied toi p,olarduplex .,wire telegraphy.. where; thetele--- graphcircuits are superposed on telephone circuits. As regardsthe transmitter the system is identical with Fig. `1.v VAt the receivingside the direct current impulses pass, however, through filters F2` tothe rejector .circuit designed as a repeater, which is equipped with`two sets or groups of choke coils or windings D1, D2, protected againsthigh voltage discharges Vor leaks from the line. In this Way the entirereceiving apparatus with the exception of the filterFz may bellocated onthe protected side of the repeater. The alternating current feeding therejector circuit D2 is through a protective repeater or transformer Ussupplied to a rectier G in the output of which there .are developedalternating currents which according to the design of the rectifier, areof the frequency of the fundamental oscillation ofthesource ofalternating current or of higher harmonics, in addition to a directcurrent Vcomponent which serves for the magnetic biasing of the chokesD, D2. The filter F3 interposed between the rectifier G `and the chokeD2 is adapted to permit direct current and one of the alternatingcurrent frequencies to pass. By way of a rectifier g2, the rejectorcircuit is connected with the impulse relay R.

v Thetransformers serving for protective purposes are preferablydesigned to be high-tensionproof and with grounded shields to thetransformer windings, as in the example described above. l

Fig. 3 illustrates a forked transformer A installed in a telegraphstation, and destined for the amplification of the `incoming currents,and an intermediate repeater B, which ampliiies the telegraph signalsarriving from the forked repeater A vand passes them on to anarrangement similar to A, not shown in the drawing.

In Fig. 3 of the drawing SG indicates an alternating current generatorwhose current is dispatched by `closing the transmitting key ST. Whenthe key is depressed toclose the circuit, this alternating current issupplied tothe recti- Iier arrangement G11 through the .transformerBetween the transmitting or sending equipment described and thereceiving apparatus designated ER is connected the vmagnetic repeaterMV, which handles the transmission of the signals sent to the outgoingline L1 and the transmission-of the signals arriving over vthis line tothe receiving apparatus ER. This magnetic repeater includes theiron-containing inductances W1 to We. A magnetic amplifier consistsgenerally of biased iron choke coils connected in the circuit of asource of high frequency. The iron chokes W1 and W2 arebiased throughthe windings W5, We, which are traversed by the direct current of thebattery `B. The high frequency supplied by the generator I-I is fed tothe chokes W1 Yand W2 through the transformer U3. The signals arrivingover the line L1 and to be amplified traverse the choke coils W1 and W2in the same direction and thereby vary the alternating currentresistance of the iron chokes for the high-frequency carrieroscillation. The carrier frequency is thus .modulated by the currents tobe amplified. The modulated oscillations are through the windings Ws andW4 and the transformer U2 passed tothe receiving apparatus ER afterrectification by means Vof the rectifier equipment G12. Thetransformation ratio of the transformer U2 is made variable to enableregulation of the repeater. Itwill be understood, however, that othermeans for controlling the degree of amplification may be used, forinstance the variation of the amplitude of the carrier frequency. Theline L1 is bridged for the carrier frequency by means of the condenserC2.

-To enable the magnetic amplifier MV to carry out its function as abalancing repeater, the choke coils W1 and W2 are each provided with amidpoint tap S1 and S2. To these taps are connected the lines leading tothe transmitting apparatus. Under the assumption that the artiflcialbalancing line N is a close simulation of the resistance connected tothe terminal points A1 and A2 of the windings W1 and W2, an-d moreparticularly of the resistance of the transmission line L1, the currentsemanating from the transmitting apparatus traverse the two halves of thewindings W1 and W2 in opposite directions and in equal strength. Thisprevents a transmission of the sending currents to the windings W3 andW4 and thus to the receiving apparatus. Due to the design of itswindings according to our inventionthe magnetic amplifier MV thus takesover the functions of a balancing repeater between the line L1 and thetransmitting and the receiving apparatus. The transmitting and thereceiving apparatus are uncoupled from each other.

As already pointed out it is necessary to prevent the direct currentarriving over the line L1 and traversing the rectifier G11 (the incomingcurrent), from being modulated by the outgoing current of saidrectifier. For this purpose the transmitter key ST is according to ourinvention bridged by the adjustable bridging resistance UW. As a`further means for eliminating the said modulation there is connected incircuit behind the rectifier G11, a variable attenuation member D in theform of a bridged T-connection. The attenuation member may at the sametime be used as a frequency correcting device.

The intermediate repeater contains the repeaters MV1 and MV2 destinedfor the two different directions of traffic. The repeater MV1 ampliiiesin the direction A-B and the repeater MV2 in the opposite direction. Thetwo magnetic repeaters are of a construction similar to that of therepeater described at A, so that a detailed description appearssuperfluous. They act at the same time as balancing repeaters so thatthe signals amplified by MV1, for instance, which are supplied to theamplifier MV2 at its points of symmetry S2, are only returned into theline L2 and not amplified by the repeater MV2 to the magnetic repeaterMV1.

At D3 and D4 adjustable attenuation membersH are indicated, which areintended to partly neutralize the eifect of the variable outputimpedance of the vrectiiiers G11 and G12, and at the Sametime serve tocontrol the frequencies of the repeater circuit. The direct currentgenerators G1 and G2 supply direct current which serves for thecompensation of the direct current taken by the rectifiers G11 and G12.Similarly, a direct current generator G3 is associated with the variableattenuation member D.

For the sake of completeness there is in this diagram of connectionsalso provided a twowire intermediate repeater SV for the ampliiicationof the superposed speech currents, which is connected to the two linesL1 and L2 through the-repeaters or transformers SU1 and SU2respectively. The condensers KL1 and KL2 and the coil lines SL1, SLzserve in a well known manner for the separation of the telegraph andtelephone currents. Y

To explain the mode ofoperation ofthe in-v termediate `repeater circuitsthe transmission of telegraph signals in the direction A-B will now beconcisely described. The telegraph signals arriving over the line L1pass over the coil line SL1 into the magnetic repeater MV1, in whichtakes place a modulation of the carrier oscillations supplied `by thesource Vof high frequency current Vv`H1. Then modulatedV oscillationsare through the transformer U1 supplied to the rectifier GL1, in whoseoutput circuit there' eXistthe telegraph currents arriving over L1 withamplified amplitude, and which are passed through the attenuationapparatusDa to the symmetry points S2 ofthe repeater MYX2. Assuming aclose simulation of the line L2 by the artificial balancing line Nz'theamplified currentsV pass from the stymmetrypoints S2 through the coil'line Sie into the line L2 Without generating amplified currents in theoutput Vof the magnetic repeater MVz. y ItY will rbe readily understoodthat as a matter ofcourse modifications in the connections described maybe made without departing fro-m the ambitof ourappended claims. Thus thewindings W2, W4 and Ws of the magnetic repeater shown at vA may, forinstance, be omitted.' In the same'way it would be possible to replacethe attenuation circuit D by asimpler connection.

We claim as our invention:

1. Telegraphic repeater system, more particu- Ylarlyfra 'Wire telegraphsystem, including telegraph apparatus, transformers so connected as tovprotect the telegraph apparatus against disturbing voltages on theline, said transformers being located at the sending and at thereceivingends of the line, an alternating current circuit at theVsending end of the line, a key for opening and closing said circuit,rectifier apparatus interposed between the sending transformer and Ithe' line, whereby the alternating current signals produced byVVoperating said key will` be converted into direct current signals,

Y whichY are sent over the line, arreceiving circuit located beyond thetransformerat the receiving end of the line, and a device locatedbetween said transformer and the line, for converting the direct currentsignals intov alternating current signals, which pass' through the saidtransformer into the receiving circuit.

2." 'Ielegraphic repeater system, more, particularly a wire telegraphsystem, including telegraph apparatus, transformers so connected as toprotect the telegraph apparatus against disturbing voltages onjthe line,an alternating current circuit, means for opening and closing saidcircuit, rectifier apparatus interposed between thetransforrner at thesending station and the line to convert the alternating current impulsesproduced by the 'operation of said means into direct current signals, amagnetic amplifier including choke coils connected with the line, a

source of alternating current'connected with said coils, a transformerconnected with said amplier, a receiving relay, land rectifyingapparatus interposed between saidtransformer and said relay. g t Y Y 3.In a repeater system for Vwire telegraphy of the polar-duplex type,including telegraph .apparatus, transformers so connected as to protectVthe telegraph apparatus against disturbing voltages on the line,a'magnetic amplifier adapted to amplify the telegraph signals, a doubleline' constituting a 'transmission channel common to both directions oftraffic; two transmission channelseach constitutingY a one-Way line, andan artificial balancing line connected with said doubleline,Ysaidamplifier having coils so designed and connected with said linesthat it will actV asa balancing repeater between the three transmissionchannels. v p

4. Ina repeater system for wire telegraphy of the polar-duplex type,including telegraph apparatus, transformers so connected as to protectSthe telegraph apparatus against disturbing voltages on the line, analternating current circuit, means for opening and closing said circuit,a rectifier vfor converting alternating. current impulses produced insaid circuit, into direct current impulse telegraphA signals, a magneticamplifier adapted to amplify the telegraph signals, yand an adjustableattenuation member connected in parallel with said rectifier.

5. In a repeater system for Wire telegraphy of the polar-duplex type,including telegraph apparatus, transformers so lconnected as to protectthe telegraph apparatus against disturbing voltages on the line, amagnetic amplifier adapted to amplify the telegraph signals, and abiased one-way rectifier connected-in shunt to said amplifier. e

V6. In a telegraph system, more particularly a system of compositetelegraphy and telephony, a metallic line circuit adapted to transmitdirect current impulses, a transmitting circuit comprising a source ofalternating current and means for transmitting telegraph signals fromsaid source of current, a transformer inductively connecting saidtransmitting circuit with said line circuit and adapted to protect saidtransmitting circuit from disturbing voltages on said line circuit, andrectifying means interposed between said transformer and said linecircuit for converting alternating current telegraph signals transmittedfrom said transmittingcircuit into direct current signals which are tobe sent lover the line.

7, In a duplex telegraph system, more particularly a system of compositeduplex telegraphy and telephony, a metallic line circuit adapted totransmit direct currentV impulses in Aboth directions, a transmittingcircuit comprising means for transmitting direct current telegraphsignals into said line circuit, a receiving circuit for receiving directcurrent telegraph signals from said line circuit, an artificial linebalancing out said line circuit, and a magnetic amplifier between saidline circuit and .said receiving circuit for amplifying incoming directcurrentv telegraph signals, said magnetic ampliier comprising aplurality of coils in inductive relation to each other and in connectionwith said artificial line operating as a hybrid coil for coupling saidtransmitting circuit with said line circuit and uncoupling it from saidreceiving circuit.

8. In a duplex` telegraph system, more particularly a system ofcomposite duplex telegraphy and telephony, a metallic line circuitadapted to transmit direct current impulses in both directions, atransmitting circuit comprising means for transmitting direct currenttelegraph signals into said line circuit, a receiving circuit forreceiving direct current telegraph signals from said line circuit, amagnetic amplifier interconnected between said three circuits,comprising ra plurality of coils operating as a hybrid coil arrangementfor uncoupling the receivingcircuit from the transmitting circuit, andasource of direct current for magnetically biasing the coils of said'magnetic amplifier to sucha degree that the amplitude of the outputcurrent of said ampliiier, in the absence of telegraph signals, will notfall down to zero.

9. In a duplex telegraph system, more particularly a system of compositeduplex telegraphy and telephony, a metallic line circuit adapted totransmit direct current impulses'in both directions, a transmittingcircuit comprising means for transmitting direct current telegraphsignals into said line circuit, a receiving circuit for receiving directcurrent telegraph signals from said line circuit, a magnetic amplierinterconnected between said three circuits, comprising a plurality ofcoils operating as a hybrid coil arrangement for uncoupling thereceiving circuit from the transmitting circuit, and a source of directcurrent for magnetically biasing the coils of said magnetic amplier tosuch a degree that the amplitude of the output current of saidamplifier, in the absence of telegraph signals, will be higher than zerobut not higher than about one third of the maximum amplitude.

l0. In a duplex telegraph system, more particularly a system ofcomposite duplex telegraphy and telephony, a metallic line circuitadapted to transmit direct current impulses in both directions, atransmitting circuit comprising a source of alternating current and asending key for producing alternating current telegraph signals fromsaid source of current, rectifying means adapted to convert saidalternating current signals into direct current signals and to send theminto said line circuit, a receiving circuit for receiving direct currenttelegraph signals from said line circuit, a magnetic amplifier betweensaid line circuit and said receiving circuit comprising a plurality ofcoils arranged as a hybrid transformer for uncoupling the receivingcircuit from said transmitting circuit, and a resistance connected withsaid sending key, said resistance being of such a value that the outputcurrent of said transmitting circuit will never fall down to zero.

11. In a duplex telegraph system, more particularly a system ofcomposite duplex telegraphy and telephony, a metallic line circuitadapted to transmit direct current impulses in both directions, atransmitting circuit comprising means for producing alternating currenttelegraph signals, rectifying means adapted to convert said alternatingcurrent signals into direct current signals and to send them into saidline circuit, an attenuation network interconnectedbetween saidrectifying means and said line circuit, a receiving circuit forreceiving direct current telegraph signals from said line circuit, ahybrid coil arrangement for uncoupling said receiving circuit from saidtransmitting circuit, and a source of direct current connected with theoutput of said attenuation network for compensating for a steady outputcurrent of said rectifying means.

12. In a duplex telegraph system, more particularly a system ofcomposite duplex telegraphy and telephony, a metallic line circuitadapted to transmit direct current impulses in both directions, atwo-way repeater device interconnected between two sections of said linecircuit, said two-way repeater device consisting of two magnetic one-wayamplifiers, two hybrid coil arrangements, each connecting the sendingcircuit of one of said magnetic ampliers and the receiving circuit ofthe other with one of said two line sections and uncoupling saidreceiving circuit from said sending circuit, a source of direct currentfor magnetically biasing said magnetic ampliers, and means for adjustingsaid biasing current to such a value as to avoid back-coupling electswithin the two-way repeater device.

.13. In a duplex telegraph system, more particularly a system ofcomposite duplex telegraphy and telephony, a metallic line circuitadapted to transmit direct current impulses in both directions, atwo-way repeater device interconnected between two sections of said linecircuit, said two-way repeater device consisting of two magnetic one-wayampliers, two hybrid coil arrangements, each connecting the sendingcircuit of one of said magnetic ampliers and the receiving circuit ofthe other with one of said two line sections and uncoupling saidreceiving circuit from said sending circuit, and one-way rectiersconnected in shunt to said magnetic amplifiers, said rectifiers being sobiased as to reduce the amplication factor at low amplitudes and therebyavoid back-coupling effects within said two-way repeater device.

14. Telegraphic repeater system, more particularly a wire telegraphsystem, including telegraph apparatus, a transformer so connected as toprotect the telegraph apparatus against disturbing voltages on the line,van alternating current circuit, a key for opening or closing saidcircuit, rectier apparatus interposed between said transformer and theline, whereby the alternating current signals produced by operating saidkey will be converted into direct current signals, which are sent overthe line, a choking device located at the receiving end of the line, andmeans for feeding said device with alternating current, whereby suchdevice will convert the direct current signals into alternating currentsignals.

15. A telegraph system including a conducting line for the transmissionof direct current impulses, a transmitting circuit comprising a sourceof alternating current and means for transmitting telegraph signals fromsaid source of current, a transformer inductively connected with saidconducting line and adapted to protect said transmitting circuit fromdisturbing voltages on said conducting line, rectifying means interposedbetween said transformer and said conducting line for convertingalternating current telegraph signals transmitted from said transmittingcircuit into direct current signals which are to be sent over the line,means for reconverting said direct current signals at the receiving endof the line into alternating current signals, and a receiver responsiveto such reconverted signals.

16. A telegraph system including a conducting line for the transmissionof direct current impulses, a transmitting circuit comprising a sourceof alternating current and means for transmitting telegraph signals fromsaid source of current, a transformer inductively connected with saidconducting line and adapted to protect said transmitting circuit fromdisturbing voltages on said conducting line, rectifying means interposedAbetween said transformer and said conducting line for convertingalternating current telegraph signals transmitted from said transmittingcircuit into direct currentsignals which are to be sent over the line,means for reconverting said direct current signals at the receiving endof the line into alternating current signals, a receiver responsive todirect current signals, and rectifying means interposed between saidreconverting means and said receiver.

KARL ETZRODT.

WALTER vHEINRICH FiimNG.

